#include <iostream>
using namespace std;
class Point {
protected:
  int x, y;

public:
  Point(int a, int b = 0) {
    x = a;
    y = b;
    cout << "constructing point(" << x << "," << y << ")" << endl;
  }
};
class Line : public Point {
protected:
  int len;

public:
  Line(int a, int b, int l) : Point(a, b) { //构造函数初始化列表
    len = l;
    cout << "Constructing Line,len ..." << len << endl;
  }
};
int main() {
  Line L1(1, 2, 3);
  
}
